J&viiwceros, Gerdtorhi-nus, and Atelodus. As there are so few
existing species the subdivision of animals which agree in so
many and such, highly -characteristic features seems to be an
unnecessary procedure. The existing Rhinoceroses are but a
fragment of the total number of known forms from past epochs.
The family is very markedly on the wane.
The genus Mhinoeeros is characterised by its heavy build and
thick, almost smooth, skin — smooth, that is to say, so far as con-
cerns the slight development of hair — which is often thrown into
folds. There is one or there are two horns on the fore-part of
the head, which are, as has already been pointed out, structures
sui generis, and not exactly comparable with the horns of other
living Ungulates. There are three nearly equal toes on both
fore- and hind-limbs. The canine teeth of existing species have
disappeared; the incisors are, or are not, present; the molars and
prenaolars are three and four in each half of each jaw.
The visceral anatomy of the Rhinoceros has been nrach inves-
tigated so far as concerns the Asiatic forms, A curious feature,
which serves to discriminate some of the Asiatic species from
others, is to be seen in the small intestine. In Hh. indicus *
this gut is furnished with numerous long cylindrical narrow out-
growths " like tags of worsted " ; in the allied J£h. sondaicus these
tags are present, but are natter and broader ; -while in the two-
horned Jffi/b. sum&tTensis there are no tags at all, but only smooth
valve-like folds. Another mark by which these species can be
distinguished depends upon the variation in the presence or
absence of certain glands imbedded in the integument of the foot
— the so-called " hoof glands." These occur in Mh* indicus and
JSk. soTidawus, but are absent in Mh, sumatrensis.
Sir W. Flower2 studied some years since the skull features
which serve to differentiate the existing forms.
In Rh. sumatreTisis the two long downward processes of the
sqoamosal bone, termed respectively post-glenoid and post-
fcympanic, do not unite below the auditory meatus. In this the
species in question agrees with the African forms but not with
the one-homed Asiatic species, where the two processes completely
ifasa Again, another character, though perhaps less important,
Soe« 1873, p. 92 ; «*. 1877, p, 707. Beddard and Treves,